Sorry if this seems overcomplicated, but I believe you're doing this in the most efficient manner possible. We actually haven't gotten many related requests, although we do get requests to see other types of list history data. Our data structure currently doesn't store much history for lists particularly and that's why you have to go through another avenue, like getting the email campaigns first like you are. Storing more list history would be a rather large feature and/or infrastructure change for us, but I will pass on your feedback!